Aussies grab relay gold at swim titles

Trailing by a body length, Cate Campbell has produced a stunning anchor leg to help Australia upstage an all-star United States and claim 4x100m mixed medley relay gold at the world swimming titles.

It was Australia's third gold medal at the halfway mark of the eight-day titles at Gwangju, South Korea.

Campbell had it all to do in the final leg, diving into the pool a body length behind Simone Manuel, but she remarkably reeled in the American to touch in front of the Olympic 100m champion by 0.02 of a second.

It was Campbell's second gold at the meet after shining in Australia's 4x100m freestyle relay win on Sunday's opening night.

"I feel like a bear who has been in hibernation. I was starting to get a little bit restless in the apartment," Campbell said.

"I was like 'come on let me out, let's start racing again, there are only so many episodes of Friends I can watch'."

Campbell tried to play down her effort that helped Australia claim the mixed medley world titles for the first time in just the third time the event has been held.

The 4x100m mixed medley relay will feature at the Olympics for the first time at 2020 Tokyo.

"I knew that it was going to be a really tight race but I had to stick to my race plan ...and back myself to get the job done," she said.

Australia were tipped to win gold medal number three earlier on night four but Ariarne Titmus was upstaged by Italian veteran Federica Pellegrini in the 200m freestyle final.

At 30 years old, Pellegrini defended her world title by clocking 1:54.22 to hold out teenager Titmus by 0.44 of a second.

Titmus was the hot favourite after the withdrawals of main threats Katie Ledecky of the United States, Australia's Emma McKeon and Canada's Commonwealth Games champion Taylor Ruck.

The 18-year-old appeared to be the one to beat after a shock 400m freestyle win over American great Ledecky on Sunday night.

She was aiming to become the first Australian woman to claim the 200m-400m freestyle double at a world titles.

"I am second in the world which is great but I have high standards," Titmus said.

"Obviously I would have loved to get the gold but I wasn't good enough tonight."

Meanwhile, Jack McLoughlin produced a personal best but finished fourth in the 800m freestyle final, missing out on bronze by half a second.

The 800m title was claimed by Italy's Gregorio Paltrinieri with controversial three-time world champion Sun Yang of China finishing sixth.

Olympic champion Kyle Chalmers was second fastest qualifier for the 100m freestyle final, Kaylee McKeown was fourth fastest for the 50m backstroke final and Larkin was fifth quickest for the 200m individual medley medal race.